The present invention relates to a magnetic resonance system for obtaining a Z-spectrum of a CEST (Chemical Exchange Saturation Transfer) imaging technique, and a method applied to the magnetic resonance apparatus.
Recently, a method that attracts attention for observing a low-concentration compound is a CEST (Chemical Exchange Saturation Transfer) imaging technique, which takes advantage of signal decay resulting from chemical exchange.
CEST imaging performs a sequence while changing the frequency of an RF pulse, and generates a Z-spectrum based on data acquired by the sequence. The signal value in the Z-spectrum decays in the vicinity of the frequency at which a CEST effect is brought about. Therefore, by identifying at what frequency the signal decays from the Z-spectrum, information on CEST that depends upon the concentration of a compound or the rate of magnetization exchange may be obtained.
The Z-spectrum, however, has a dominating downward peak in the vicinity of the resonance frequency of water, which represents a Lorentz distribution of free water. The peak width of the peak is proportional to a transmission magnetic field B1, and the peak value reaches down to as low as near zero. Therefore, a signal lowering caused by CEST is buried in the downward peak representing the Lorentz distribution of free water, resulting in a problem that it is difficult to pick up information reflecting the effect of CEST from the Z-spectrum.
Therefore, there is the need for a technique for obtaining a spectrum suitable for obtaining information on CEST.